Climate–Soil–Management Interactions Regulate Soil Organic Carbon in West African Agricultural Soils

Abstract

Soil organic carbon (SOC) regulation in West African agricultural soils remains poorly constrained because climatic, mineralogical, nutrient and management controls are often evaluated separately. This study assessed the integrated controls of SOC using 749 harmonised observations of 0–20 cm soils from agricultural lands across eight West African countries. Climatic predictors included mean annual precipitation (MAP) and mean annual temperature (MAT), while edaphic variables included clay, Fe and Al oxides, cation exchange capacity (CEC), pH and total nitrogen (N). Management indicators comprised crop residue retention, manure application, fertiliser use and erosion status. Hierarchical regression, interaction modelling, variance partitioning and XGBoost with SHAP interpretation were used to evaluate additive, conditional and nonlinear controls. The final interaction model explained 75.9% of SOC variability, outperforming climate-only, edaphic + N and management-only models. MAP was the dominant climatic predictor, whereas MAT had no independent main effect. Fe oxides, Al oxides, CEC and N were positively associated with SOC, indicating the importance of mineral stabilisation and carbon–nitrogen coupling. Significant interactions among MAP × Fe oxides, MAT × pH, MAP × crop residue and MAP × erosion indicated that SOC responses depended on soil and management conditions. XGBoost confirmed strong SOC–N coupling, while a sensitivity model excluding N retained strong predictive performance (R² = 0.78) and identified MAP, Al oxides, Fe oxides, pH and CEC as major predictors. Variance partitioning showed that climatic, edaphic and management domains contributed both unique and shared explanatory fractions. Overall, SOC variability in West African agricultural soils is best explained by interacting processes of moisture-driven carbon input, mineral stabilisation, nutrient coupling and management context.